Issues with the gears, chain is jumping or slipping but only when under load

This is normally caused by one of three things,

  1. The gears are out of adjustment, either with cable tension, alignment of the mech or poor cables – in which case can be fixed on site.
  2. The chain has worn so badly that is jumping off the teeth of the cassette when you apply pressure, some gears will be fine, others will jump all the time – in this case, you are looking at new chain, cassette, jockey wheel and potentially chainrings at the front.  – In this instance I would need to take the bike away for repair
  3. The chain and cassette are not worn, and the gears are adjusted correctly, however, things are still jumping, or even the pedals are rotating totally but the power is not getting to the wheel – in this instance the Freehub has failed (or is starting to fail). The rear wheel needs to be stripped down and the freehub replaced or overhauled.  This will only be done in the workshop – so you need to book a collection.